1. Field of the Invention
The present invention relates to a spin transistor, and more particularly, to a spin transistor having a ferromagnetic source/drain and a semiconductor channel.
2. Description of the Related Art
A spin transistor (or a spin FET) as one of several new-concept devices for solving the physical limitations of conventional electronic devices has widely been researched. Since a spin transistor using a two-dimensional electron gas (2-DEG) layer as a channel was proposed by Datta and Das in 1990 (see Applied Physics Letter, vol 56, 665, 1990), research into the transport (spin injection) of spin-polarized electrons and research into adjusting the spin precession of the spin-polarized electrons have been progressing in a hybrid structure in which a semiconductor is combined with a ferromagnetic material.
In order to perform a basic operation of a spin transistor using electron spin precession, spin-polarized electrons should be essentially injected from the ferromagnetic into semiconductor, and a gate electrode should be ultimately used to control the spin precession of the spin-polarized electrons injected into the 2-dimensional electron gas channel. In this case, a spin-orbit interaction in the 2-dimensional electron gas channel should be high in order to effectively control the spin precession, and a suitable electric resistance between the ferromagnetic and the semiconductor should be maintained to observe a spin injection signal in an electrical manner. The intensity of the spin-orbit interaction may be quantified by employing a spin-orbit coupling constant (α) that may be obtained by an SdH (Shubnikov de Haas) oscillation experiments. Up to now, a channel structure based on an InAs 2-DEG layer has been known as a materials that best satisfies the above-mentioned requirements.
A semiconductor technology based on silicon is prominent in a modern industry. The semiconductor is designed and manufactured based on MOSFET (metal oxide semiconductor field effect transistor). The conventional transistor based on the semiconductor controls electrical charges in the semiconductor by using an electrical field, while a spin transistor controls both the electrical charges and the spin. There are attempts to using the spin transistor in a switching device, a logic circuit, and the like by controlling the spin-polarized electrons. When there is an electrical field E that is vertical to a wave vector k of electrons moving in the 2-DEG channel, a magnetic field is formed as HRashba ∝k×E by the spin-orbit interaction. This is referred to as the Rashba effect. When current flows in an x direction and the electrical field is applied in a z direction by a gate voltage, a magnetic field induced by a spin-orbit interaction effect is formed in a y direction. The spin-polarized electrons injected into the channel of the spin transistor begin spin precession by the magnetic field and the gate voltage can be used to adjust a precession angle.
In order to supply the electrical charges to the 2-DEG channel that links a source and a drain of the spin transistor with each other, a carrier supply layer may be formed below the channel. Such a structure is known as an inverted structure. However, in the known spin transistor structure in which the carrier supply layer is positioned below the channel, a variation of a potential gradient of the channel is limited and there is therefore a limit to acquiring high spin-orbit interaction.